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- From: Kurt Roeckx <kurt@roeckx.be>
- Date: Sun, 28 Jan 2018 15:44:08 +0100
- Subject: Check the size of the main data
-
- The main data to decode a frame can come from the current frame and part of the
- previous frame, the so called bit reservoir. si.main_data_begin is the part of
- the previous frame we need for this frame. frame_space is the amount of main
- data that can be in this frame, and next_md_begin is the part of this frame that
- is going to be used for the next frame.
-
- The maximum amount of data from a previous frame that the format allows is 511
- bytes. The maximum frame size for the defined bitrates is at MPEG 2.5 layer 2
- at 320 kbit/s and 8 kHz sample rate which gives 72 * (320000 / 8000) + 1 = 2881.
- So those defines are not large enough:
- # define MAD_BUFFER_GUARD 8
- # define MAD_BUFFER_MDLEN (511 + 2048 + MAD_BUFFER_GUARD)
-
- There is also support for a "free" bitrate which allows you to create any frame
- size, which can be larger than the buffer.
-
- Changing the defines is not an option since it's part of the ABI, so we check
- that the main data fits in the bufer.
-
- The previous frame data is stored in *stream->main_data and contains
- stream->md_len bytes. If stream->md_len is larger than the data we
- need from the previous frame (si.main_data_begin) it still wouldn't fit
- in the buffer, so just keep the data that we need.
-
- --- a/layer3.c
- +++ b/layer3.c
- @@ -2688,6 +2688,11 @@ int mad_layer_III(struct mad_stream *str
- next_md_begin = 0;
-
- md_len = si.main_data_begin + frame_space - next_md_begin;
- + if (md_len + MAD_BUFFER_GUARD > MAD_BUFFER_MDLEN) {
- + stream->error = MAD_ERROR_LOSTSYNC;
- + stream->sync = 0;
- + return -1;
- + }
-
- frame_used = 0;
-
- @@ -2705,8 +2710,11 @@ int mad_layer_III(struct mad_stream *str
- }
- }
- else {
- - mad_bit_init(&ptr,
- - *stream->main_data + stream->md_len - si.main_data_begin);
- + memmove(stream->main_data,
- + *stream->main_data + stream->md_len - si.main_data_begin,
- + si.main_data_begin);
- + stream->md_len = si.main_data_begin;
- + mad_bit_init(&ptr, *stream->main_data);
-
- if (md_len > si.main_data_begin) {
- assert(stream->md_len + md_len -
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